In the study of apparent motion of celestial bodies to a varying degree of accuracy to determine their position in the points of observation. It is not necessary to know the distance to them, because all the bodies seem to us, as it were located on the inner surface of a sphere of arbitrary radius. Therefore, the visible, the provisions of stars can only be defined directions, and their relative position - angles between these directions, or the corresponding arcs of great circles on a sphere, which emanate from the center of all the directions. An imaginary sphere of arbitrary radius centered at an arbitrary point in space, which is located on the surface of the light so they are visible in the sky at some time point in space from the villa, called the celestial sphere. Thus, the imaginary observer at the center of the celestial sphere, the situation should be seen shining on its surface in exactly the same relative positions in which the observer sees a real real lights in the sky. The rotation of the celestial sphere follows the rotation of the sky. Celestial sphere is used to study the apparent positions and motions of celestial bodies. To do this, on the surface of the main line and fixed point with respect to which, and made the necessary measurements. Direct ZOZ '(4) passing through the center of the celestial sphere and coincides with the direction of a plumb-line filaments in place of observation is called a vertical or horizontal line. Plumb line intersects with the surface of the celestial sphere in two points: at the height Z, above the head of the observer, and in a diametrically opposite point - the nadir of Z '. The big circle of the celestial sphere (SWNE), whose plane is perpendicular to the plumb line, is called a mathematical or real horizon. Mathematical horizon divides the surface of the celestial sphere into two halves: the visible to the observer, with the apex at the zenith Z, and invisible, with the apex at the nadir of Z '. Mathematics should be distinguished from the horizon of the visible horizon (the line along which the "sky is convergent with the Earth"). The apparent horizon on the land - the wrong line, a point which lies above, below the true horizon. In the open sea the visible horizon is always a small circle whose plane is parallel to the plane of the mathematical horizon. Small circle of the celestial sphere (AMA), light passing through M and the plane which is parallel to the plane of the mathematical horizon is almucantars star. Large semi-circle of the celestial sphere ZMZ ', passing through the zenith and nadir M star, called a range of heights, vertical circle, or just verticals star. Diameter PP '(5) around which the rotation of the celestial sphere, called the axis of the world. The axis of the world intersects with the surface of the celestial sphere in two points: at the north pole of the world P and the south pole of the world P '. North Pole one of the rotation of the celestial sphere which is clockwise when viewed from outside the area. The big circle of the celestial sphere QWQ'E, whose plane is perpendicular to the axis of the world, called the celestial equator. The celestial equator divides the surface of the celestial sphere into two hemispheres: the north, with the north pole of the world P and south, with the south pole of the world P '. Small circle of the celestial sphere (bMb), a plane which is parallel to the plane of the celestial equator is called the celestial or heavenly body parallel diurnal M. Apparent diurnal motion of stars are made on a daily parallels. Large semi-circle of the celestial sphere PMP ', passing through the poles of the world and shone through M, is called the hour circle and the declination circle of lights. The celestial equator intersects with the mathematical horizon in two points: at the point E, and east to the west of the point W. Circles of altitude, passing through the point of east and west, called the first verticals - east and west. The big circle of the celestial sphere PZQSP'Z'Q'N, the plane which passes through the sheer line and the axis of the world, is called the celestial meridian. Celestial meridian divides the surface of the celestial sphere into two hemispheres: the eastern, east to a point E, and west, with a point west of W. The plane of the celestial meridian and the plane of the mathematical horizon intersect in a straight line of NOS, which is called the noon line. Celestial meridian intersects with the mathematical horizon in two points: at the north N and south of the point S. The point of the north is the one that is closer to the north pole of the world. The point of the south - closer to the south pole of the world. Celestial meridian intersects the celestial equator in two points: at the top of the equator Q, which is closer to the zenith, and the lowest point of the equator, Q ', which is closer to the nadir. Doug celestial meridian PZQSP 'is its upper part, and the arc PNQ'Z'P' - the lower

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